I just found the article on Lucas additives in the Self help section and it really sheds the light on the issue. I never realized that an additive would actually cause the lube to trap air like it does.

Indeed, back in the day of the 4 speed tranny, the cases and seals were low quality, I ran STP straight in my 1960 FL, it shifted hard when cold but did not leak too bad, tho I would not use this in any of the modern 5 or 6 speeds

Ya no....Its funny you should ask this....Just last week I sat down with the king himself ,,Richard petty ...Over the period of several hours and beers we discussed his racing and the use of STP...I asked the king if he would recommend using STP in our bikes...He said .....................................Well...I cant tell you what he said..:shock.....A short time later in my visit his son Kyle showed up and he said he wouldn't run the STP in any of his bikes and went on to say more but the language was so bad I had to leave.....Sorry for the long anser.....Id tell you all about our bike ride another time....Mat